Transport refrigeration system

Abstract

A transport refrigeration system of the type which can provide either cooling or heating includes a pressure regulating valve 42 controlling hot gas to the evaporator during a heating cycle and operable to prevent an excessive suction pressure, and a pressure regulating valve 74 between the two outlet sides of a three-way valve and operable to pass refrigerant from the hot gas line 34 to the condenser 30 when the hot gas pressure is excessive, the arrangement limiting the values of both the evaporator suction pressure and the hot gas discharge pressure to prevent overloading in heating and defrost operations.

I claim: 
     
       1. In a transport refrigeration unit of the type adapted to selectively provide either cooling or heating, a refrigeration system including: a three-way valve having an inlet, and first and second outlets;   a refrigerant compressor having a discharge line connected to supply said three-way valve;   a refrigerant condenser;   a refrigerant evaporator;   first refrigerant line means connecting the first outlet of said three-way valve to said condenser for operation of the system in a cooling mode when said three-way valve is in a first position;   hot gas refrigerant line means connecting the second outlet of said three-way valve for passage of hot gas to said evaporator in operation of the system in a heating or defrost mode when said three-way valve is in said second position;   a pressure regulating valve in said hot gas line means to control refrigerant amounts to limit evaporator pressure to a first predetermined value;   a relief valve connected between said first line means and said hot gas line means and operable, when said three-way valve is in said second position, to pass refrigerant to said first line and said condenser when the hot gas pressure exceeds a second predetermined value;   whereby the values of both evaporator pressure and discharge pressure are limited to prevent overloading in heating and defrost operations.   
     
     
       2. In a unit according to claim 1 wherein: said system includes a refrigerant expansion device of the pressure limiting type for limiting suction pressure, and operable in a cooling mode to prevent overloading.   
     
     
       3. A unit according to claim 1 wherein: said pressure regulating valve is responsive to the suction pressure leaving said evaporator.